Balanced Charge and Discharge Control for Asymmetric Dual Battery System

ABSTRACT

In some examples, a system includes a primary side with a charger and a first battery and a secondary side with a second battery. The charger on the primary side can charge both the first battery and the second battery. A hinge resistance is between the primary side and the secondary side. The primary side includes a feedback controlled active device in a current path of the first battery that compensates for the hinge resistance, for connector resistances, or for battery impedances in a current path of the second battery.

TECHNICAL FIELD

This disclosure relates generally to balanced charge and dischargecontrol for an asymmetric dual battery system.

BACKGROUND

Dual display converged mobility devices are increasingly used in mobilecomputing. Use of a device with dual display may require batteries oneither side of the device in order to achieve battery life required topower both displays.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description may be better understood byreferencing the accompanying drawings, which contain specific examplesof numerous features of the disclosed subject matter.

FIG. 1 illustrates a system in accordance with some embodiments;

FIG. 2 illustrates a graph illustrating battery voltage and batterycapacity;

FIG. 3 illustrates a graph illustrating battery voltage and batterycapacity in accordance with some embodiments;

FIG. 4 illustrates battery charge termination voltage adjustment inaccordance with some embodiments;

FIG. 5 illustrates a system in accordance with some embodiments;

FIG. 6 illustrates a system in accordance with some embodiments;

FIG. 7 illustrates a system in accordance with some embodiments;

FIG. 8 illustrates a system in accordance with some embodiments;

FIG. 9 illustrates a system in accordance with some embodiments;

FIG. 10 illustrates a system in accordance with some embodiments;

FIG. 11 illustrates a system in accordance with some embodiments.

In some cases, the same numbers are used throughout the disclosure andthe figures to reference like components and features. In some cases,numbers in the 100 series refer to features originally found in FIG. 1;numbers in the 200 series refer to features originally found in FIG. 2;and so on.

DETAILED DESCRIPTION

Dual display converged mobility devices are increasingly used in mobilecomputing. Use of a device with dual display may require batteries oneither side of the device in order to achieve battery life required topower both displays. For compact devices, a 1S2P battery configurationprovides a space optimized energy management solution. A 2Sconfiguration, dual charger approach, etc., for example, can be morecomplex and consume more space. Design of hinges connecting both sidesmechanically and electrically can be extremely space constrained.Additionally, wires connecting the batteries in parallel can offerconsiderable resistance due to wire gauge limitations. To keep cost andelectrical complexity under control, most printed circuit board (PCB)electronics can be placed on one side, with required electronics placedon the other side (for example, a second display, touch, audio, etc.)This can lead to asymmetric board and battery sizes and loads.

In some embodiments, a charger solution on one side (for example, theprimary side or motherboard side) can be optimized, since elements suchas a power management integrated circuit (PMIC) and Universal Serial Bus(USB) ports such as USB Type-C ports can be located on one side (such asthe motherboard side, for example). However, when the charger is on oneside, in order to run wires through to the other side in a foldablesystem, very thin wires may be run through the foldable portion of thedevice, creating hinge resistances and/or impedances due to the foldableportions and hinge resistances, for example. Due to hinge resistancesand/or impedances, battery charging currents to the battery on the sidewith the charger and to the battery on the other side from the chargerare different than expected. For example, the battery on the side withthe charger may take a higher charge current than the battery on theother side without the charger. This occurs, for example, due to voltagedrops across the hinge resistance, and the current that should flow tothe far battery will not flow to that battery. Some of that excesscurrent may even flow into the battery on the side with the charger (forexample, the battery on the primary or motherboard side). This situationcan lead to imbalanced charging. For example, the battery on the sidewith the charger will become fully charged while the battery on theother side is still charging. The battery on the side with the chargermay then become more charged than necessary during each chargingoperation while waiting for the other battery to charge, which is notgood for the battery that is being charged more than necessary. This isparticularly troublesome in situations where the battery on the chargingside is smaller, an issue in situations where the charger is on themotherboard side, for example, since batteries on the motherboard sideare often smaller due to space constraints on that side of the system.

During battery discharge, since loads on the side with the charger (forexample, the primary side, main board side, or motherboard side) can bemuch larger than on the secondary side, and also due to hingeresistances, for example, the battery on the side with the charger canbe discharged much faster than the battery on the other side. Thebattery on the charger side may be discharged while the battery on theother side still has charge. For example, in the case of batteries withthe same capacity, 10-15% of capacity may still exist on the secondaryside while the capacity on the primary charger side may be close to 0%.Battery impedance imbalances may occur along with large voltage dropsacross the hinge resistances, which can result in system shutdowns.Also, currents on the primary charger side may be increased, and mayhave most of the current due to, for example, voltage drops across thehinge resistances. The battery on the other side may not be able tosupport a large portion of the discharge current. Therefore, in someembodiments, discharge balancing may be implemented.

FIG. 1 illustrates a system 100 that includes a primary side 102 (forexample, a motherboard side) and a secondary side 104. In someembodiments, system 100 can be included in a dual display device (forexample, used in mobile computing). Use of a device with dual displaymay require batteries on either side of the device in order to achievebattery life required to power both displays. In some embodiments, forexample, the primary side 102 can be a side of the system 100 includinga first display and the secondary side 104 can be a side of the system100 including a second display (for example, system 100 can be a dualdisplay device with displays on two different sides of the device).

Primary side 102 includes main board loads 122, charger 124, battery 126(Battery1), and an inductor 128. Charger 124 includes a transistor 132(for example, a field effect transistor or FET). Secondary side 104includes secondary side loads 142, battery 146 (Battery2) and anoptional field effect transistor (FET) 148. FET 148 can be used toreduce the VSYS2 voltage drop.

In some embodiments, battery 126 on the primary side 102 and battery 146on the secondary side 104 can be 1S batteries coupled in parallel thatare charged by a single charger 124 located on the primary side 102.System 100 can also include hinge resistance HR1 162 (for example, 100mOhm), hinge resistance HR2 164 (for example, 100 mOhm), and hingeresistance HR3 166 (for example, 100 mOhm). In some embodiments, system100 is a foldable device with the primary side 102 and the secondaryside 104, where the sides can be folded relative to each other (forexample, at the point of the hinge resistances).

In some embodiments, charging current driven from the charger 124 ofsystem 100 may not be equally distributed until the battery with thehigher current (either battery1 126 or battery2 146) increases itsvoltage due to faster charging. This can be due to an additional voltagedrop in the VBAT path VBAT2 (battery voltage path) and GND path GND2(ground voltage path) for battery 146. In system 100, battery1 126 maybe smaller (for example, located on the motherboard side), and ends uptaking most of the charging current at the beginning of charging. Duringnormal discharge, battery1 126 may be at a lower state of charge due toa hinge resistance drop from battery2 146. In some embodiments, theremay be a risk of over charge current trip by a protection device inbattery1 126. In some embodiments, a fast charging time can considerablyincrease as battery1 126 reaches constant voltage (CV) earlier andbattery2 146 reaches CV at a later time. In some embodiments, battery1126 may wear out faster than battery2 146 due to exposure to highercharger currents and much lower termination currents (for example,battery1 126 reaches CV earlier). In some embodiments, fast chargingtime also increases due to limiting the maximum total charging currentto ensure that the batteries 126 and 146 do not lock out due to highcurrent. In some embodiments, if charger 124 input VIN is plugged out(not plugged in) during charging, both batteries 126 and 146 will be atdifferent charging levels, and this may cause circulating currentsbetween batteries 126 and 146. It can also limit the peak currents thatthe battery packs together can drive to load.

FIG. 2 illustrates a system 200 with charge imbalance. System 200includes a first battery pack 202 on the left side of FIG. 2 and asecond battery pack 204 on the right side of FIG. 2. First battery pack202 includes a battery1 (BAT1) 222 and a resistor 224 (for example, witha resistance of 75 mOhms). Second battery pack 204 includes a battery2(BAT2) 224 and a resistor 244 (for example, with a resistance of 75mOhms). System 200 also includes a hinge resistor 262 (for example, witha resistance of 50 mOhms).

System 200 includes a total hinge resistance of 50 mOhms, for example(VBAT and GND paths). In some embodiments, battery1 (BAT1) 222 on theleft of FIG. 2 has a capacity of, for example, 1500 mAH, and battery2(BAT2) 242 on the right of FIG. 2 has a capacity of 2500 mAH. Each ofthe battery packs 202 and 204 in system 200 includes, for example, aninternal resistance of 75 mOhms. It is noted that both battery packs 202and 204 may have similar resistance, where most of the resistance is dueto protection circuits. In an example of system 200, a charger isdriving a total charge current of 4 Amp (for example, 1C charging).Battery voltages in system 200 can be equal and well below the CVcharging levels.

In some embodiments, system 200 is a foldable device with the primaryside and the secondary side, where the sides can be folded relative toeach other (for example, at the point of the hinge resistance 262). Insome embodiments, without charge balancing, an impact occurs due tohinge resistance 262. For example, at the beginning of charging, BAT1222 current may be 2.5 A and BAT2 242 current may be 1.5 A due to thehinge resistance drop. BAT2 242 current may be close to 1.7C (that is1.7 times the charge current), and this may trip the maximum chargecurrent protection of BAT1 222. This initial charge current canconsiderably reduce the BAT1 222 life. If normal charging stillcontinues, after some time of charging, the charging current may becomeproportional to battery capacities (for example, IBAT1=1.5 A andIBAT2=2.5 A) due to self-balancing. When the voltage at the chargeroutput is at CV (constant voltage charging) level (for example, 4.2V),the following may occur, for example: VBAT1=4.2V and VBAT2=3.89V. VBAT2voltage may still be very far from CV voltage when VBAT1 hits CVvoltage. That is, when battery2 242 hits the termination current in CVmode, battery2 242 charge current may be far below its specifiedtermination current level. This can also impact the BAT1 222 life.

In some embodiments, in order to solve some or all of the abovechallenges, for example, charge currents may be equally distributed toboth batteries irrespective of hinge resistance, contact resistances,and battery impedance. In some embodiments, charge current may bedistributed in the same ratio as the battery capacities.

In some embodiments, an independent battery charger may be used for eachbattery with independent charge control of each battery. However, withindependent chargers for each battery, cost and space requirements maybe higher. Additionally, it may be tough to manage discharge ofbatteries without wasting power if one charger supplies input power tothe other charger.

In some embodiments, current limiting of each battery charge current maybe implemented to keep the batteries from seeing excessive chargecurrents. Current limiting each battery charge current may beimplemented in a manner that the current may be programmed at a fixedlevel. This can prevent battery overcharge protection from beingactivated, but the charge current to each battery may not be balanced.However, fast charging time may considerably increase as the firstbattery reaches constant voltage (CV) earlier than the second battery,which reaches constant voltage at a later time. Additionally, one of thebatteries may wear out faster due to exposure to higher charger currentsand much lower termination currents.

In some embodiments, a 2S approach may be used where the batteries arewired in a 2S configuration. This can make sure that both batteries willsee the same charge/discharge currents. However, with battery capacitieson both side being different, charge balancing is a major challenge.Cost/space/efficiency optimized power solutions may not be availableusing a 2S approach.

A primary reason for improper charge current distribution can be, forexample, hinge resistance, connector resistance, and/or batteryimpedance in VBAT and GND paths for one of the batteries (for example,battery2) from the charger. In some embodiments, a feedback controlledactive device can be added in the current path of one of the batteries(for example, in the battery1 current path) that introduces a resistancein the battery current path (for example, the battery1 current path)that compensates for hinge resistance(s), connector resistance(s),and/or battery impedance(s) in another battery path (for example, in thebattery2 current path).

In some embodiments, a single conventional 1S charger may be used. Insome embodiments, charge current may be automatically distributedirrespective of the total current from the battery charger due tofeedback control. This distribution can also be active when the currentreduces in a CV mode (constant voltage mode). In some embodiments,accurate, capacity based charge current distribution may be implementedusing very little extra circuit space. In some embodiments, largecurrent flow from a secondary battery (for example, battery2) to aprimary battery (for example, battery1) may be prevented during assemblyby limiting the current.

FIG. 3 illustrates a system 300 in accordance with some embodiments. Insome embodiments, system 300 includes a charge current distributioncircuit. In some embodiments, the circuit within the dashed lines inFIG. 3 is a charge current distribution circuit.

In some embodiments, FIG. 3 illustrates a system 300 that includes aprimary side 302 (for example, a motherboard side) and a secondary side304. In some embodiments, system 300 can be included in a dual displaydevice (for example, used in mobile computing). Use of a device withdual display may require batteries on either side of the device in orderto achieve battery life required to power both displays. In someembodiments, for example, the primary side 302 can be a side of thesystem 300 including a first display and the secondary side 304 can be aside of the system 300 including a second display (for example, system300 can be a dual display device with displays on two different sides ofthe device).

Primary side 302 includes main board loads 322, charger 324, battery 326(Battery1), and an inductor 328. Charger 324 includes a transistor 332(for example, a field effect transistor or FET). Secondary side 304includes secondary side loads 342, battery 346 (Battery2) and anoptional field effect transistor (FET) 348. FET 348 can be used toreduce the VSYS2 voltage drop.

In some embodiments, battery 326 on the primary side 302 and battery 346on the secondary side 304 can be 1S batteries coupled in parallel thatare charged by a single charger 324 located on the primary side 302.System 300 can also include hinge resistance HR1 362 (for example, 100mOhm), hinge resistance HR2 364 (for example, 100 mOhm), and hingeresistance HR3 366 (for example, 100 mOhm). In some embodiments, system300 is a foldable device with the primary side 302 and the secondaryside 304, where the sides can be folded relative to each other (forexample, at the point of the hinge resistances).

Improper charge current distribution may occur due to hinge resistance,connector resistance, and/or battery impedance. For example, impropercharge current distribution may occur due to hinge resistance, connectorresistance, and/or battery impedance in VBAT and GND paths from acharger to a battery (for example, in VBAT and GND paths from thecharger 324 illustrated in FIG. 3 to battery2 346 illustrated in FIG.3).

In some embodiments, a feedback controlled active device may be includedin the battery1 326 current path. A feedback controlled active deviceincluded in the battery1 326 current path can compensate for hingeresistance(s), connector resistance(s), and/or battery impedance(s) inthe battery2 346 path. For example, in some embodiments, system 300includes a feedback controlled active device (for example, in someembodiments, the circuit 372 illustrated in FIG. 3 on the primary side302 that is included in dashed lines can be a feedback controlled activedevice). In some embodiments, a circuit 372 such as a feedbackcontrolled active device can be included in the battery1 326 currentpath and can introduce resistance in the battery1 326 current path thatcan compensate for hinge resistance(s), connector resistance(s), and/orbattery impedance(s) in the battery2 346 current path. In someembodiments, resistors RS1 374 and/or RS2 376 are included in thefeedback controlled active device 372. In some embodiments, resistor RS1374 may have a resistance of 10 mOhm, for example. In some embodiments,resistor RS2 376 may have a resistance of 10 mOhm, for example. In someembodiments, resistor RS1 374 and/or resistor RS2 376 sense the currentthrough each of the battery current paths. In some embodiments, an erroramplifier 378 (for example, Error Amp1) and a field effect transistor380 (FET1) can be included in the feedback controlled active devicecircuit 372. In some embodiments, an error amplifier (such as Error Amp1378) can adjust FET1 380 resistance to ensure that sense resistors RS1374 and RS2 376 drop equal voltages. This can ensure that equal currentsto battery1 326 and battery2 346 (or distributed currents based on theRS1 374 and RS2 376 resistor values). In some embodiments, the circuit372 included in the dashed lines in FIG. 3 shows some circuit elements.It is noted that additional components may be included in the system 300(for example, within the circuit 372 illustrated by dashed lines in FIG.3) to help provide, for example, feedback compensation, rail to railsense, error amplifier power in dead battery mode, etc.

In some embodiments, during assembly, the secondary side 304 can beassembled after a certain amount of testing with only the battery 326 onthe primary side 302. In some embodiments, the primary battery 326 canbe at a lower charge level than the secondary battery 346. In someembodiments, a feedback controlled active device (for example, thecircuit 372 in the dashed lines in FIG. 3) can prevent at assembly alarge current flow from the battery2 346 on the secondary side 304 tothe battery1 326 on the primary side 302 by limiting the current. Insome embodiments, transistor FET1 380 of FIG. 3 may fully turn offduring assembly, and the resistor Rmax 382 can limit the current fromthe secondary side battery2 346. In some embodiments, the resistance ofresistor Rmax 382 is 0.2 Ohms. In some embodiments, depending on systemdesign, the resistance of resistor Rmax 382 can be adjusted based on adesired maximum charge sharing current limit.

In some embodiments, error amplifier 2 (Error Amp2) 384 can override andmake transistor FET1 380 fully on during discharge conditions. Chargebalancing may only be needed during battery charging when the currentthrough sense resistor RS1 374 and sense resistor RS2 376 are positive.In some embodiments, diode D1 386 can indicate that error amplifier 2(Error Amp2) 384 can override error amplifier 1 (Error Amp1) 378 onlyfor turning on transistor FET1 380 and not for turning off. In someembodiments, this logic may be implemented in different ways.

In some embodiments, system 300 includes two current sense resistors 374and 376, a FET 380 with a bypass resistor 382, and two operationalamplifiers 378 and 384. In some embodiments, battery1 326 and battery2346 are the same size. In such a situation it is advantageous thatcharge currents of batteries 326 and 346 are the same. Therefore, insome embodiments, the voltage drop across resistor RS1 374 and thevoltage drop across RS2 376 are the same. Therefore, in someembodiments, when the voltage drops across RS1 374 and RS2 376 are thesame, the input voltage to error amplifier Amp1 378 is zero. Erroramplifier Amp1 378 can control transistor FET1 380 in a linear state.However, it can add a small impedance (assistance) to make sure that animpedance from both batteries 326 and 346 to the charger 324 output willbe equal.

Operational assistance for the battery voltage is generated by FET1 380through a closed loop control controlled by error amplifier Amp1 378. Inthis manner the impedance through FET1 380 can be used to match theimpedance at VBAT2. In some embodiments, the input to Amp1 378 ismaintained at zero, and the voltage drop across RS1 374 is maintained tobe the same as the voltage drop across RS2 376. This helps to maintainsimilar currents into battery1 326 and battery2 346, even as current toeach battery varies during charging.

In some embodiments, amplifier Amp2 384 can override amplifier Amp1 378(for example, when charging is removed and current is flowing in theopposite direction than current flow during charging. During dischargeof battery1 326, for example, current may flow through transistor 332 ofthe charger 324 and to the VSYS node to provide power to main boardloads 322, for example. During discharging, the voltage across resistorRS2 376 is reversed relative to the voltage across resistor RS2 376during charging, and the output of error amp2 384 is zero. In thissituation, D1 386 pulls FET1 380 to low to turn it fully ON. In thismanner, during battery discharge, FET1 380 is fully ON and amplifier 384overrides amplifier 378 to ensure no additional impedance (other than inRS1 374 and RS2 376) during discharge. Different arrangements arepossible in different embodiments, but in some embodiments, a transistorsuch as FET1 380 is added at VBAT1 to match VBAT2 power.

FIG. 4 illustrates flow 400 in accordance with some embodiments. In someembodiments, flow 400 implements charge current balancing. In someembodiments, flow 400 beings at 402. At 404 a determination is made asto whether an input source is ready. If an input source is not ready at404, charging is disabled at 406 and flow returns to 404. If an inputsource is ready at 404, a determination is made at 408 as to whether acharge current is positive at resistor RS1 374, for example. If thecharge current is not positive at 408, charge balancing is disabled at410 (for example, FET1 378 is kept fully ON) and flow returns to 408. Ifthe charge current is positive at 408, active charge current balancingis enabled at 412, and flow returns to 404.

In some embodiments, charge balancing 400 is enabled only when thecharge current through RS1 374 is positive, for example. This can besensed by the Error Amp2 384. Error Amp2 384 can be configured tooverride Error Amp1 376, or the same function can be implemented bycontrolling an enable input for Error Amp1 376 using an output fromError Amp2 384. It is noted that other implementations in accordancewith some embodiments other than that illustrated in FIG. 3 and/or FIG.4 can also be implemented.

In some embodiments, once the charge current to each battery isbalanced, charger levels (for example, charge CV levels) can beincreased to compensate for the total voltage drop from the chargeroutput to the battery terminal. Once the state of charge is above 80%,for example, CV voltage can again be adjusted to meet the batteryrequirement to reduce charging time.

FIG. 5 illustrates a charge current distribution circuit 500 inaccordance with some embodiments. In some embodiments, charge currentdistribution circuit 500 can be included in system 300 (for example, inplace of some or all of the circuit 372 illustrated within dashed linesin FIG. 3).

In some embodiments, charge current distribution circuit 500 is a ratiometric charge current distribution circuit. In some embodiments, chargecurrent distribution circuit 500 can accurately balance charge currentbased on the battery capacity without choosing different current senseresistor values. At 10 mOhm range of sense resistance, it can bedifficult to get fine resolution.

Circuit 500 includes resistor R1 502, resistor R2 504, resistor RS1 574,resistor RS2 576, error amplifier 578 (for example, Error Amp1), fieldeffect transistor 580 (FET1), resistor Rmax 582, error amplifier 2(Error Amp2) 584, and diode D1 586. In some embodiments, resistor RS1574, resistor RS2 576, error amplifier 578 (for example, Error Amp1),field effect transistor 580 (FET1), resistor Rmax 582, error amplifier 2(Error Amp2) 584, and diode D1 586 can be the same as or similar toresistor RS1 574, resistor RS2 576, error amplifier 578 (for example,Error Amp1), field effect transistor 580 (FET1), resistor Rmax 582,error amplifier 2 (Error Amp2) 584, and diode D1 586. In someembodiments, resistor RS1 374, resistor RS2 376, error amplifier 378(for example, Error Amp1), field effect transistor 380 (FET1), resistorRmax 382, error amplifier 2 (Error Amp2) 384, and diode D1 386,respectively. In some embodiments, circuit 500 can be used in a systemin which battery2 (BAT2) is of a bigger capacity than battery1 (BAT1).However, it is noted that the circuit can be swapped in case battery1(BAT1) is of a bigger capacity than battery2 (BAT2). In someembodiments, resistor R1 502 and resistor R2 504 of circuit 500 candivide voltage across sense resistor RS1 574. In some embodiments, aresistance of sense resistor RS1 574 can be, for example, 10 mOhm. Theerror amplifier 578 can adjust the currents to ensure that voltageacross resistor R1 502 is equal to voltage across R2 504. In someembodiments, a ratio of the resistances of resistor R1 502 and resistorR2 504 can be adjusted to get the required results.

In some embodiments, the charge current distribution circuit within thedashed lines in system 300 and/or the charge current distributioncircuit 500 can be adjusted. That is, in accordance with someembodiments, measuring the charge current to each battery and thenadjusting the impedance of the active device in the battery1 path can beimplemented in different ways.

In some embodiments, system 300 can be a simple solution due to thecurrent sense on the same side. However, in accordance with someembodiments, current sense information from a fuel gauge sense resistorfrom the secondary side can be brought to the primary side. This maysave, for example, an additional RS1 resistor and an additional voltagedrop across RS1 during charge and discharge. In some embodiments, RS2can be used for current sense for a fuel gauge (fuel gauge1) on theprimary side with a positive supply current sensing fuel gauge to avoidadditional voltage drop in the battery1 path.

It is noted that hinge resistance from a higher capacity secondary sidebattery to a primary side processor board can considerably reducemaximum currents (for example, maximum power limit currents, maximum PL4currents, and/or maximum power limit 4 currents) that can be drawn bythe system, especially when the battery state of charge is low.

In some embodiments resistor R1 502 and resistor R2 504 are added acrossresistor RS1 574 in circuit 372 as illustrated in FIG. 5. In someembodiment, instead of sensing the right hand side of resistor RS1 574,amplifier 578 senses the mid-point of resistor R1 502 and resistor R2504. This implementation may be used when battery1 326 and battery2 346are not the same size (for example, if battery1 326 is smaller thanbattery2 346, or if battery2 346 is smaller than battery1 326). Ifbattery1 326 is smaller than battery2 346, for example, then thebattery2 346 current needs to be higher. For example, if a capacity ofbattery1 326 is one unit and a capacity of battery2 346 is two units,for example, twice as much current may need to be sent to battery2 346than the current sent to battery1 326 (for example, 2 A to battery2 346and 1 A to battery1 326). In this situation, if the resistance of R1 502and the resistance of R2 504 are equal, the control loop can ensure thatbattery2 346 can get twice the current provided to battery1 326.Resistances of R1 502 and R2 504 can be adjusted according to capacitiesof battery1 326 and battery2 346 to make sure that the current providedto each of the batteries 326 and 346 is equal. In an embodiment wherecapacities of battery1 326 and battery2 346 are equal, resistor R1 502can be open and a resistance of R2 504 can be zero to ensure that thesame currents are applied to each battery.

FIG. 6 illustrates a system 600 with a first (primary side) battery pack602 and a second (secondary side) battery pack 604. System 700 caninclude a total hinge resistance 662 of 50 mOhms, for example. In someembodiments, system 600 is a foldable device with the primary side andthe secondary side, where the sides can be folded relative to each other(for example, at the point of the hinge resistance 662). The firstbattery pack 602 includes a first battery1 (BAT1) 622 and a resistor624. The second battery pack 604 includes a second battery2 (BAT2) 642and a resistor 644. The primary side battery 622 (for example, battery1or BAT1) and the secondary side battery 642 (for example, battery2 orBAT2) can be connected in parallel. System 600 can include a total hingeresistance 622 of 50 mOhms, for example. In some embodiments, battery1(BAT1) 622 on the left of FIG. 6 has a capacity of, for example, 1500mAH, and battery2 (BAT2) 642 on the right of FIG. 6 has a capacity of2500 mAH. In some embodiments, both batteries 622 and 642 can be lithiumion (Li ion) rechargeable type batteries. Each of the battery packs 602and 604 in system 600 can include, for example, an internal resistance624 and 644, respectively (for example, each with an internal resistanceof 75 mOhms). In an example of system 600, if the system is trying todraw a maximum possible power with a limited minimum system voltage (forexample, limited to 3V), it is possible to draw a current (for example,it is possible to draw a current of 12.8 Amp). Out of the example 12.8Amp, 8 Amp may be contributed by the primary side battery 622 and 4.8Amp may be contributed by the secondary side battery 642, for example.

Primary side battery current may exceed 3C limits (for example, 3 timescapacity or charge current C limits such as for example, 4.5 Amp), andcan cause a trip if the current lasts for too long of a time period (forexample, is the current lasts for 10 ms). At the same time the system isunable to fully use the secondary side battery (for example, 3C=7.5Amp). It is noted that 3C is used as an example limit. In someembodiments, for example, depending on the battery, other example limitsmay be 2C or 4C, or in a range of 2C to 4C.

Without discharge balancing, the system will have to limit total currentsuch that the primary side battery current is, for example, less than4.5 Amp (for example, less than 3C). Total system current might belimited to 7.2 Amp (1.8C of the total capacity). In some embodiments,turbo performance may be increased, for example, by 66% (for example, to12 A rather than 7.2 A) with discharge balancing and proper currentsharing (for example, proper 3C current sharing, or other limit currentsharing). This may be implemented in a manner that is independent of thebattery state of charge.

When battery impedance increases near the end of charge, turbo may befurther limited due to minimum system voltage and/or due to the additionof hinge resistance.

Useful capacity issues may also occur. For example, instantaneousdischarge current drawn from each battery may depend on load profile,battery impedance, hinge resistance, and/or which side to which the loadis connected, etc. If the primary load is larger, primary display sidebattery may become empty while the secondary display side battery mightstill have remaining charge.

FIG. 7 illustrates a system 700 with a first (primary side) battery pack702 and a second (secondary side) battery pack 704. The first batterypack 702 includes a first battery1 (BAT1) 722 and a resistor 724. Thesecond battery pack 704 includes a second battery2 (BAT2) 742 and aresistor 744. The primary side battery (for example, battery1 or BAT1)722 and the secondary side battery (for example, battery2 or BAT2) 742can be connected in parallel. System 700 can include a total hingeresistance 762 of 50 mOhms, for example. In some embodiments, system 700is a foldable device with the primary side and the secondary side, wherethe sides can be folded relative to each other (for example, at thepoint of the hinge resistance 762). In some embodiments, battery1 (BAT1)722 on the left of FIG. 7 has a capacity of, for example, 1500 mAH, andbattery2 (BAT2) 742 on the right of FIG. 7 has a capacity of 2500 mAH.In some embodiments, both batteries 722 and 742 can be lithium ion (Liion) rechargeable type batteries. Each of the battery packs 702 and 704in system 700 can include, for example, an internal resistance 724 and744, respectively (for example, both having an internal resistance of 75mOhms). In an example of system 700, the system load may be 2 A total onthe primary side. After some discharge time, battery currents may becomeproportional to the respective capacities of the batteries. Under theseconditions, the battery voltage difference might be around 100 mV. A 100mV higher voltage on the secondary side 704 may translate into aremaining charge of around 10% remaining on the secondary battery 742when the primary battery 722 is already empty.

Battery impedance seen by the system can increase drastically when theprimary side battery is fully empty and the secondary side battery stillhas some charge left. This can limit the possible peak load currentwithout causing a minimum system voltage trip. Effective batteryimpedance seen by the load may be mostly due to the secondary batteryimpedance plus the hinge resistance. In order to avoid unexpected trips,the system may not discharge until this point, thereby wasting batterycapacity. Depending on the hinge resistance, primary side load power,and other factors, the wasted charge may be in the 5-10% range.

If the primary display side load has periodic high currents (which isoften the case for computing devices), most of it can be supplied by aprimary display side battery and later replenished by a secondarydisplay side battery. The secondary side battery can charge the primaryside battery after surge current. This can increase the charge dischargecycles for the primary side battery, causing it to degrade faster.Therefore, in accordance with some embodiments, an equal distribution ofdischarge currents is made to both primary and secondary side batteriesirrespective of hinge resistance, contact resistances, and batteryimpedance. In some embodiments, the discharge current is distributed ina same ratio as a ratio of battery capacities.

A dual charger approach might be used with a second charger driving thefirst charger input voltage (VIN), for example, through a reverse boostmode form the secondary side battery (for example, battery2). The dualcharger approach may be combined with battery voltage paths (VBATpaths). In a dual charger approach, discharge from the second batterymay be highly inefficient due to boosting to 5V VBUS and then buckconversion from 5V to the primary battery voltage. The secondary batterymay be discharge fully first, when available, without adding specialcharge management control. A dual charger with combined VBAT (or VBATA)may solve the charge current balancing, but may not solve dischargecurrent balancing. That is, performance issues may occur relating tohinge resistance from a higher capacity secondary side battery to aprimary side processor board, which may considerably reduce max PL4currents that can be drawn from the system, especially when the batterystate of charge is low. Also, useful capacity issues may occur due toinstantaneous discharge current drawn from each battery depending on theload profile, battery impedance, hinge resistance, and to which side theload is connected, and if the primary load is larger, a primary displayside battery can become empty while the secondary display side batterystill has some charge left. Further, battery life issues may occur. Ifthe primary display side load has periodic high currents, most supplywill be from the primary side battery and later replenished by thesecondary side battery, and charge discharge cycles for the primary sidebattery may be increased, causing it to degrade faster.

Discharge current imbalance can occur due to hinge resistance, connectorresistance, and/or battery impedance in the VBAT and GND paths for thesecondary side battery (for example, battery2) from the charger. Inaccordance with some embodiments, a feedback controlled boost convertercan be included in the secondary side battery path (battery2 path) thatadds a series voltage in the path to compensate for voltage dropsbetween the primary side battery (battery1) and the secondary sidebattery (battery2). This can include ground path drops. In someembodiments, the battery voltages are both indirectly regulated and/ortracked at the same level during discharge. When the battery voltagestrack each other, the discharge currents may become proportional to thebattery capacities. If the feedback control loop is designed to respondfast enough battery currents can be properly shared for all practicalload conditions (for example, direct current or pulsating).

In some embodiments, a single 1S charger may be used. In someembodiments, discharge current can be automatically distributedirrespective of the battery capacities. In some embodiments, betterVBATA peak current may be obtained to support PL4 SOC loads due to theaddition of a boost converter. In some embodiments, secondary batterycurrents (battery2 currents) can be increased to a maximum level, andbattery voltage can be minimized as the secondary side loads areconnected at the output side of the boost converter. This can allow PL4performance until the battery is close to empty. In some embodiments,voltage tracking can enable discharge currents that are proportional tothe battery capacity.

FIG. 8 illustrates a system 800 in accordance with some embodiments. Insome embodiments, FIG. 8 illustrates a system 800 that includes aprimary side 802 (for example, a motherboard side) and a secondary side804. In some embodiments, system 800 can be included in a dual displaydevice (for example, used in mobile computing). Use of a device withdual display may require batteries on either side of the device in orderto achieve battery life required to power both displays. In someembodiments, for example, the primary side 802 can be a side of thesystem 800 including a first display and the secondary side 804 can be aside of the system 800 including a second display (for example, system800 can be a dual display device with displays on two different sides ofthe device).

Primary side 802 includes main board loads 822, charger 824, battery 826(Battery1), and an inductor 828. Charger 824 includes a transistor 832(for example, a field effect transistor or FET). Secondary side 804includes secondary side loads 842 and battery 846 (Battery2).

In some embodiments, battery 826 on the primary side 802 and battery 846on the secondary side 804 can be 1S batteries coupled in parallel thatare charged by a single charger 824 located on the primary side 802.System 800 can also include hinge resistance HR1 862 (for example, 100mOhm), hinge resistance HR2 864 (for example, 100 mOhm), and hingeresistance HR3 866 (for example, 100 mOhm). In some embodiments, system800 is a foldable device with the primary side 802 and the secondaryside 804, where the sides can be folded relative to each other (forexample, at the point of the hinge resistances).

In some embodiments, system 800 includes a battery discharge balancingcircuit. In some embodiments, the circuit 872 within the dashed lines inFIG. 8 is a discharge balancing circuit. In some embodiments, battery1voltage on the primary side is sensed differentially and compared withthe battery2 voltage on the secondary side using error Amp1 (erroramplifier 1) 874. The compared error can include a voltage drop on thebattery positive side and the ground side (GND side). A boost converter876 (for example, boost stage plus bypass illustrated in FIG. 8) iscontrolled using this amplified difference in voltage. In someembodiments, the boost converter 876 can effectively adjust its dutycycle to ensure that the voltage at the output is bumped up tocompensate for voltage drop in the positive and GND paths betweenbattery1 826 and battery2 846. A control loop is used to control thevoltage across the battery2 total impedance. Therefore, the loopresponse can be fast.

In some embodiments, if both batteries (battery1 and battery2) haveequal capacity, discharge may start at the same voltages and bothbatteries have equal internal impedances. The boost converter andcontrol loop can adjust until both battery impedances drop equalvoltages as the control loop adjusts until VBAT1 and VBAT2 become equal.This can control the battery currents to be equal.

In some embodiments, if the batteries (battery1 and battery2) havedifferent capacities, the batteries start at the same voltage and bothbatteries have equal internal impedances. The discharge current canstart at the same level. The battery with the lower capacity may thendeplete faster for some time, and the control loop and/or boostconverter can adjust the battery currents to be proportional to batterycapacities. The lower capacity battery may have to discharge to a lowerlevel according to the following EQUATION 1:

ΔV=BATTimp×ΔI  (EQUATION 1)

Where ΔV is an extra voltage by which the lower capacity battery needsto discharge;

Where ΔI is a difference in current to make the discharge currentproportional to the battery capacity; and

Where BATTimp is the total battery impedance excluding hinge resistance.

In some embodiments, combinations of battery impedances and capacitiesmay all converge to discharge currents proportional to batterycapacities at different ΔV values. The ΔV may be unavoidable in a 1S2Por 1SNP configuration, for example, if the battery impedance is notproportional to battery capacity. However, in some situations, practicalvalues of ΔV may be small, and can be small enough to be ignored.

In some embodiments, when the hinge resistance drop is positive on theprimary side and current is flowing from the primary side to thesecondary side, battery discharge can be balanced by operating a FET(for example, a FET on the secondary side such as FET2 878 in FIG. 8) inthe active region using a feedback loop that compares VBAT1 and VBAT2using, for example, Error Amp2 880 of FIG. 8. In some embodiments, ErrorAmp2 additionally receives an input from discharge balance logic 882.When secondary side load power dominates, if FET2 878 is fully ON,battery2 846 may discharge faster. If FET2 878 is fully OFF, battery1826 may discharge faster. By controlling current through FET2 878, it ispossible to keep VBAT1 and VBAT2 at the same voltage level duringdischarge. In some embodiments, SOC PL2/PL4 logic 884 can be used toreduce VBAT1, for example, by sensing as needed.

As described herein, in FIG. 8, a small boost control stage may beincluded. The boost control can compensate for voltage drops due tohinge resistance. Battery1 826 voltage is sensed differentially byamplifier 874, and the makes sure that battery2 846 voltage is the sameby controlling the boost. By using the boost, the battery is effectivelyplaced on the other side of the hinge resistance (that is, from a systemstandpoint, battery2 846 will appear to be at the battery1 826 side).Any drop in voltage due to hinge resistance will be compensated by theboost stage. This can ensure that each battery discharges at the samerate (or at the same current) regardless of load differences and evenduring surge currents, and can maintain each battery at the same voltagelevel.

FIG. 9 illustrates a boost converter circuit 900 in accordance with someembodiments. In some embodiments, boost converter circuit 900 can beincluded in system 800 (for example, in place of some or all of thecircuit 872 illustrated within dashed lines in FIG. 8). Circuit 900includes an error amplifier (Error Amp1) 974, a boost control 976,transistor Q1 978 (for example, a FET), transistor Q2 980 (for example,a FET), transistor Q3 982 (for example, a FET), an inductor 984, acapacitor 986, and a capacitor 988.

In some embodiments, the boost converter circuit 900 illustrated in FIG.9 is a synchronous type boost converter (for example, a regularsynchronous type boost converter). In some embodiments, transistors Q1978 and Q2 980 (for example, field effect transistors Q1 and Q2 or FETsQ1 and Q2) can form a boost converter portion. In some embodiments,transistor Q3 982 (for example, field effect transistor Q3 or FET Q3)can be a bypass transistor (or bypass FET). During normal operationtransistors Q1 978 and Q3 982 may be switching based on the requiredinductor current level for the internal loop controlled by the externalvoltage control loop. In some embodiments, transistor Q3 982 is a bypasstransistor that can be enabled during low load current levels (forexample, when the hinge resistance drop is very low and can be ignored)and during charging when the boosting function is not needed. In thismanner, losses from charging and during standby can be reduced. When thedischarge current is very small, the system is in a standby state, noactive discharge balancing is necessary, etc., Q3 can be used to put theboost control (boost converter) to sleep and wasting energy in standbymode can be avoided.

Boost converter efficiency can be very high in normal operating modes.For example, when the total system load is 1 A (˜4 W) and the secondaryside is contributing 0.5 A and compensating a 100 mV drop across thetotal hinge resistance of 200 mOhms, boost converter efficiency canreach above 95% operating at 1 MHZ using normally sized components.Efficiency can increase further if the frequency is reduced from 1 MHzfor the smaller load (for example, to 500 kHz using pulse skipping).These efficiency estimates/examples may not include losses in the hingeresistance due to voltage drops.

In some embodiments, boost converter input voltage may be controlled ina manner that does not have to compensate a right half place zerotypical to boost converters. Therefore, the loop bandwidth is notlimited to 1/3 of the right hand plane (RHP) zero, making the loopcontrol fast to track pulsating load currents.

In some embodiments, the total load current on the primary side may behigher than on the secondary side, and the current through hingeresistance may flow from the secondary side to the primary side. Thus,the boost converter may only compensate for the hinge resistance voltagedrop in one direction.

In some embodiments, when the hinge resistance drop is positive on theprimary side and current is flowing from the primary side to thesecondary side, battery discharge can be balanced by operating a FET(for example, a FET on the secondary side such as FET2 878 in FIG. 8) inthe active region using a feedback loop that compares VBAT1 and VBAT2using, for example, Error Amp2 880 of FIG. 8. When secondary side loadpower dominates, if FET2 878 is fully ON, battery2 may discharge faster.If FET2 878 is fully OFF, battery1 may discharge faster. By controllingcurrent through FET2 878, it is possible to keep VBAT1 and VBAT2 at thesame voltage level during discharge.

FIG. 10 illustrates a system 1000 in accordance with some embodiments.In some embodiments, system 1000 includes a battery discharge balancingcircuit.

In some embodiments, FIG. 10 illustrates a system 1000 that includes aprimary side 1002 (for example, a motherboard side) and a secondary side1004. In some embodiments, system 1000 can be included in a dual displaydevice (for example, used in mobile computing). Use of a device withdual display may require batteries on either side of the device in orderto achieve battery life required to power both displays. In someembodiments, for example, the primary side 1002 can be a side of thesystem 1000 including a first display and the secondary side 1004 can bea side of the system 1000 including a second display (for example,system 1000 can be a dual display device with displays on two differentsides of the device).

Primary side 1002 includes main board loads 1022, charger 1024, battery1026 (Battery1), and an inductor 1028. Charger 1024 includes atransistor 1032 (for example, a field effect transistor or FET).Secondary side 1004 includes secondary side loads 1042 and battery 1046(Battery2).

In some embodiments, battery 1026 on the primary side 1002 and battery1046 on the secondary side 1004 can be 1S batteries coupled in parallelthat are charged by a single charger 1024 located on the primary side1002. System 1000 can also include hinge resistance HR1 1062 (forexample, 100 mOhm), hinge resistance HR2 1064 (for example, 100 mOhm),and hinge resistance HR3 1066 (for example, 100 mOhm). In someembodiments, system 1000 is a foldable device with the primary side andthe secondary side, where the sides can be folded relative to each other(for example, at the point of the hinge resistances).

In some embodiments, system 1000 includes a battery discharge balancingcircuit which includes one or more (or all) of a fuel gauge 1034, asensing resistor 1036 (for example, 10 mOhm), a current sensor 1038providing an output current (“current out”), an Error Amp1 1074, a boostconverter 1076 (for example, boost stage plus bypass), a transistor (forexample, a field effect transistor FET2) 1078, an enable signal 1080 fortransistor 1078 (for example, an enable signal provided during batterydischarge), a resistor R_gain 1082, a sensing resistor 1092 (forexample, 10 mOhm), and a fuel gauge 1094.

In some embodiments, system 1000 can provide control using a boostconverter configuration including boost stage with bypass 1076. In someembodiments, the battery2 1046 inductor current may be directlycontrolled to match measured battery1 1026 current. In some embodiments,a separate current sense amplifier 1074 may be used to sense thebattery1 1026 current from the sense resistor 1036 for the fuel gauge1034, or the fuel gauge itself can provide the output current.

In some embodiments, output current is converted to voltage with respectto GND2 on the secondary side 1004, which can remove common mode noise.The gain may be adjusted in proportion to the battery capacities usingresistor R_gain 1082. In some embodiments, the average inductor currentmay be controlled while removing one pole from the control loop. Thiscan significantly improve the speed of the control loop, but accuratemeasurement of the inductor current may be difficult.

In some embodiments, in system 1000, the battery1 current is sensed andthe boost is adjusted so that the battery2 current is the same. TheIBAT1 current of battery1, the IBAT2 current of battery2, and thecurrent for the boost inductor I_INDUCTOR can all be controlled to beequal in system 1000 in embodiments where the batteries have the samecapacity. However, in situations where the batteries do not have thesame capacity, resistor 1082 R_gain can be adjusted to provide anasymmetric discharge of the batteries by varying their dischargecurrents accordingly.

FIG. 11 illustrates a system 1100 in accordance with some embodiments.In some embodiments, system 1100 includes a battery discharge balancingcircuit.

In some embodiments, FIG. 11 illustrates a system 1100 that includes aprimary side 1102 (for example, a motherboard side) and a secondary side1104. In some embodiments, system 1100 can be included in a dual displaydevice (for example, used in mobile computing). Use of a device withdual display may require batteries on either side of the device in orderto achieve battery life required to power both displays. In someembodiments, for example, the primary side 1102 can be a side of thesystem 1100 including a first display and the secondary side 1104 can bea side of the system 1100 including a second display (for example,system 1100 can be a dual display device with displays on two differentsides of the device).

Primary side 1102 includes main board loads 1122, charger 1124, battery1126 (Battery1), and an inductor 1128. Charger 1124 includes atransistor 1132 (for example, a field effect transistor or FET).Secondary side 1104 includes secondary side loads 1142 and battery 1146(Battery2).

In some embodiments, battery 1126 on the primary side 1102 and battery1146 on the secondary side 1104 can be 1S batteries coupled in parallelthat are charged by a single charger 1124 located on the primary side1102. System 1100 can also include hinge resistance HR1 1162 (forexample, 100 mOhm), hinge resistance HR2 1164 (for example, 100 mOhm),and hinge resistance HR3 1166 (for example, 100 mOhm). In someembodiments, system 1100 is a foldable device with the primary side 1102and the secondary side 1104, where the sides can be folded relative toeach other (for example, at the point of the hinge resistances).

In some embodiments, system 1100 includes a battery discharge balancingcircuit which includes one or more (or all) of a fuel gauge 1134, asensing resistor 1136 (for example, 10 mOhm), a current sensor 1138providing an output current (“current out”), an Error Amp1 1174, a boostconverter 1176 (for example, boost stage plus bypass), a transistor (forexample, a field effect transistor FET2) 1178, an enable signal 1180 fortransistor 1078 (for example, an enable signal provided during batterydischarge), a resistor R_gain 1182, a sensing resistor 1192 (forexample, 10 mOhm), a fuel gauge 1194, and/or a current sense amplifier1196 providing an output current.

In some embodiments, system 1100 may control battery1 current andbattery2 current by measuring fuel gauge sense resistor voltages (forexample, fuel gauge 1134 sense resistor 1136 voltages and/or fuel gauge1194 sense resistor 1196 voltages). In some embodiments, system 1100 mayhave a higher accuracy than system 1000, but a response of system 1100may be relatively slower than a response of system 1000 due to the extrapole added by filter capacitors. However, system 1100 can still obtainresponse times that are fast enough to meet practical load conditions.It is noted that FIG. 10 and FIG. 11 do not illustrate additional FET2related circuits that may be used for simplification of dischargebalance in accordance with some embodiments. In some embodiments, forexample, a FET2 control implementation as illustrated in FIG. 8 may beused in FIG. 10 and/or in FIG. 11 when the secondary side load isdominating, for example. This implementation may also be used inconjunction with system 1000 of FIG. 10 and/or with system 1100 of FIG.11.

In some embodiments, if the feedback control loop is not fast enough, orif more momentary surge power is desired from the secondary battery, theVBAT1 sensed voltage may be artificially reduced using SOC control. Forshort durations, maximum discharge capacity of battery2 may be utilizedto pump current to the primary side (for example, to support PL4currents). When the sensed VBAT1 voltage is low, the boost converter mayincrease the current draw from the secondary battery (battery2) to meetthe altered VBAT1 sensed voltage.

In some embodiments, secondary side loads may be connected to the outputside of the boost converter (for example, in system 800, system 1000and/or system 1100). This can make sure that there is no risk ofviolating minimum system voltage and unexpected trips. Thus, in someembodiments, there is no need to use one more additional control wireconnection from the primary side to the secondary side to enable SOCcontrolled surge power supply from battery2 to the primary side. TheVBAT1 sense line itself may be used to manipulate the sense voltage toenable this feature.

Reference in the specification to “one embodiment” or “an embodiment” or“some embodiments” of the disclosed subject matter means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment of thedisclosed subject matter. Thus, the phrase “in one embodiment” or “insome embodiments” may appear in various places throughout thespecification, but the phrase may not necessarily refer to the sameembodiment or embodiments.

Example 1

In some examples, a system includes a primary side with a charger and afirst battery and a secondary side with a second battery. The firstbattery is to provide power to the primary side. The second battery toprovide power to the secondary side. A hinge resistance is between theprimary side and the secondary side. The charger is to charge the firstbattery and the second battery. The primary side includes a feedbackcontrolled active device in a current path of the first battery thatcompensates for one or more of the hinge resistance, connectorresistances, or battery impedances in a current path of the secondbattery.

Example 2 includes the subject matter of example 1. In example 2, theprimary side includes a motherboard of the system.

Example 3 includes the subject matter of any of examples 1-2. In example3, the first battery is to provide power to a first display of thesystem and the second battery is to provide power to a second display ofthe system.

Example 4 includes the subject matter of any of examples 1-3. In example4, the feedback controlled active device includes a first sense resistorto sense current through a battery current path of the first battery anda second sense resistor to sense current through a battery current pathof the second battery.

Example 5 includes the subject matter of any of examples 1-4. In example5, the feedback controlled active device includes an amplifier and atransistor, the amplifier to adjust a resistance of the transistor sothat voltage drops across the first sense resistor and the second senseresistor are equal during a charging of the first battery and the secondbattery.

Example 6 includes the subject matter of any of examples 1-5. In example6, the transistor is a field effect transistor.

Example 7 includes the subject matter of any of examples 1-6. In example7, the feedback controlled active device includes a second amplifier tooverride the first amplifier during a discharging of the first batteryand the second battery.

Example 8 includes the subject matter of any of examples 1-7. In example8, the second amplifier is to turn the transistor fully on during thedischarging of the first battery and the second battery.

Example 9 includes the subject matter of any of examples 1-8. In example9, the feedback controlled active device includes a bypass resistoracross the transistor.

Example 10 includes the subject matter of any of examples 1-9. Inexample 10, the bypass resistor is to be adjusted based on a maximumcharge sharing current limit.

Example 11 includes the subject matter of any of examples 1-10. Inexample 11, the feedback controlled active device includes a firstresistor and a second resistor coupled in series with each other, theseries connection of the first resistor and the second resistor coupledin series to be coupled in parallel with the first sense resistor,wherein resistances of the first resistor and the second resistorcoupled in series with each other can be adjusted to adjust chargingcurrents of the first battery and the second battery.

Example 12 includes the subject matter of any of examples 1-11. Inexample 12, the feedback controlled active device is to balance chargingand discharging of the first battery and the second battery.

Example 13

In some examples, a system includes a primary side with a charger and afirst battery and a secondary side with a second battery. The firstbattery is to provide power to the primary side. The second battery isto provide power to the secondary side. The system includes hingeresistance between the primary side and the secondary side. The chargeris to charge the first battery and the second battery. The secondaryside includes a feedback controlled boost converter in a current path ofthe second battery that compensates for voltage drops between the firstbattery and the second battery.

Example 14 includes the subject matter of example 13. In example 14, theprimary side includes a motherboard of the system.

Example 15 includes the subject matter of any of examples 13-14. Inexample 15, the first battery is to provide power to a first display ofthe system and the second battery is to provide power to a seconddisplay of the system.

Example 16 includes the subject matter of any of examples 13-15. Inexample 16, the feedback controlled boost converter includes a seriesvoltage in the current path of the second battery to compensate forvoltage drops between the first battery and the second battery.

Example 17 includes the subject matter of any of examples 13-16. Inexample 17, the feedback controlled boost converter includes anamplifier to differentially sense a voltage of the first battery andcompare it with a voltage of the second battery.

Example 18 includes the subject matter of any of examples 13-17. Inexample 18, the amplifier is to control the boost converter using theamplified difference in voltage.

Example 19 includes the subject matter of any of examples 13-18. Inexample 19, the boost converter is to adjust a duty cycle to compensatefor a voltage drop between the first battery and the second battery.

Example 20 includes the subject matter of any of examples 13-19. Inexample 20, if a capacity of the first battery is the same as a capacityof the second battery, the feedback controlled boost converter is todischarge the first battery and the second battery at equal voltages andat equal currents.

Example 21 includes the subject matter of any of examples 13-20. Inexample 21, if a capacity of the first battery is not the same as acapacity of the second battery, the feedback controlled boost converteris to adjust a discharge current of the first battery and a dischargecurrent of the second battery to be proportional to their respectivebattery capacities.

Example 22 includes the subject matter of any of examples 13-21. Inexample 22, the feedback controlled boost converter includes a currentsense amplifier to sense a current of the first battery and to controlthe boost converter in response to the sensed current of the firstbattery.

Example 23 includes the subject matter of any of examples 13-22. Inexample 23, the feedback controlled boost converter includes a currentsense amplifier to sense a current of the first battery, to sense acurrent of the second battery, and to control the boost converter inresponse to the sensed current of the first battery and the sensedcurrent of the second battery.

Example 24 includes the subject matter of any of examples 13-23. Inexample 24, the feedback controlled boost converter is to maintain adischarge current of the first battery and a discharge current of thesecond battery to be equal.

Example 25 includes the subject matter of any of examples 13-24. Inexample 25, the feedback controlled boost converter is to automaticallydistribute discharge current to the first battery and to the secondbattery irrespective of battery capacities.

Example 26

In some examples, a system includes a primary side with a means forcharging and a first battery, and a secondary side with a secondbattery. The first battery is to provide power to the primary side. Thesecond battery is to provide power to the secondary side. A hingeresistance is between the primary side and the secondary side. The meansfor charging is to charge the first battery and the second battery. Theprimary side includes a means for controlling feedback in a current pathof the first battery including means for compensating for one or more ofthe hinge resistance, connector resistances, or battery impedances in acurrent path of the second battery.

Example 27 includes the subject matter of example 26. In example 27, theprimary side includes a motherboard of the system.

Example 28 includes the subject matter of any of examples 26-27. Inexample 28, the first battery is to provide power to a first display ofthe system and the second battery is to provide power to a seconddisplay of the system.

Example 29 includes the subject matter of any of examples 26-28. Inexample 29, the feedback controlled active device includes a first meansfor sensing current through a battery current path of the first batteryand a second sense resistor to sense current through a battery currentpath of the second battery.

Example 30 includes the subject matter of any of examples 26-29. Inexample 30, the feedback controlled active device includes means foramplifying and a transistor, the means for amplifying to adjust aresistance of the transistor so that voltage drops across the firstsense resistor and the second sense resistor are equal during a chargingof the first battery and the second battery.

Example 31 includes the subject matter of any of examples 26-30. Inexample 31, the transistor is a field effect transistor.

Example 32 includes the subject matter of any of examples 26-31. Inexample 32, the means for controlling feedback includes a secondamplifier to override the first amplifier during a discharging of thefirst battery and the second battery.

Example 33 includes the subject matter of any of examples 26-32. Inexample 33, the second amplifier is to turn the transistor fully onduring the discharging of the first battery and the second battery.

Example 34 includes the subject matter of any of examples 26-33. Inexample 34, the means for controlling feedback includes a bypassresistor across the transistor.

Example 35 includes the subject matter of any of examples 26-34. Inexample 35, including means for adjusting the bypass resistor based on amaximum charge sharing current limit.

Example 36 includes the subject matter of any of examples 26-35. Inexample 36, the means for controlling feedback including a firstresistor and a second resistor coupled in series with each other, theseries connection of the first resistor and the second resistor coupledin series to be coupled in parallel with the first sense resistor,wherein resistances of the first resistor and the second resistorcoupled in series with each other can be adjusted to adjust chargingcurrents of the first battery and the second battery.

Example 37 includes the subject matter of any of examples 26-36. Inexample 37, the means for controlling feedback including means forbalancing charging and discharging of the first battery and the secondbattery.

Example 38

In some examples, a system includes a primary side with means forcharging and a first battery, and a secondary side with a secondbattery. The first battery is to provide power to the primary side. Thesecond battery is to provide power to the secondary side. The systemincludes hinge resistance between the primary side and the secondaryside. The means for charging is to charge the first battery and thesecond battery. The secondary side includes a boost converting means forcontrolling feedback in a current path of the second battery thatcompensates for voltage drops between the first battery and the secondbattery.

Example 39 includes the subject matter of example 38. In example 39, theprimary side includes a motherboard of the system.

Example 40 includes the subject matter of any of examples 38-39. Inexample 40, the first battery is to provide power to a first display ofthe system and the second battery is to provide power to a seconddisplay of the system.

Example 41 includes the subject matter of any of examples 38-40. Inexample 41, the boost converting means for controlling feedbackincluding a series voltage in the current path of the second battery tocompensate for voltage drops between the first battery and the secondbattery.

Example 42 includes the subject matter of any of examples 38-41. Inexample 42, the boost converting means for controlling feedbackincluding means for amplifying to differentially sense a voltage of thefirst battery and compare it with a voltage of the second battery.

Example 43 includes the subject matter of any of examples 38-42. Inexample 42, the amplifier is to control the boost converter using theamplified difference in voltage.

Example 44 includes the subject matter of any of examples 38-43. Inexample 43, including means for adjusting a duty cycle to compensate fora voltage drop between the first battery and the second battery.

Example 45 includes the subject matter of any of examples 38-44. Inexample 45, if a capacity of the first battery is the same as a capacityof the second battery, including means for discharging the first batteryand the second battery at equal voltages and at equal currents.

Example 46 includes the subject matter of any of examples 38-45. Inexample 46, if a capacity of the first battery is not the same as acapacity of the second battery, means for adjusting a discharge currentof the first battery and a discharge current of the second battery to beproportional to their respective battery capacities.

Example 47 includes the subject matter of any of examples 38-46. Inexample 47, wherein the boost converting means for controlling feedbackincludes a current sense amplifier to sense a current of the firstbattery and to control the boost converter in response to the sensedcurrent of the first battery.

Example 48 includes the subject matter of any of examples 38-47. Inexample 48, the boost converting means for controlling feedback includesa current sense amplifier to sense a current of the first battery, tosense a current of the second battery, and to control the boostconverting means in response to the sensed current of the first batteryand the sensed current of the second battery.

Example 49 includes the subject matter of any of examples 38-48. Inexample 48, including means for maintaining a discharge current of thefirst battery and a discharge current of the second battery to be equal.

Example 50 includes the subject matter of any of examples 38-49. Inexample 50, including means for automatically distributing dischargecurrent to the first battery and to the second battery irrespective ofbattery capacities.

Example 51

In some examples, a primary side includes a charger and a first batteryand a secondary side includes a second battery. A hinge resistance isbetween the primary side and the secondary side. The primary sideincludes a feedback controlled active device in a current path of thefirst battery that compensates for the hinge resistance, for connectorresistances, or for battery impedances in a current path of the secondbattery.

Example 52

In some examples, a primary side includes a charger and a first batteryand a secondary side includes a second battery. A hinge resistance isbetween the primary side and the secondary side. The secondary sideincludes a feedback controlled boost converter in a current path of thesecond battery that compensates for voltage drops between the firstbattery and the second battery.

Example 53

In some examples, an apparatus including means to perform a method orrealize an apparatus as in any other example.

Example 54

In some examples, machine-readable storage including machine-readableinstructions, when executed, to implement a method or realize anapparatus as in any other example.

Example 55

In some examples, one or more machine readable medium including code,when executed, to cause a machine to perform the method or realize anapparatus of any other example.

Although example embodiments and examples of the disclosed subjectmatter are described with reference to circuit diagrams, flow diagrams,block diagrams etc. in the drawings, persons of ordinary skill in theart will readily appreciate that many other ways of implementing thedisclosed subject matter may alternatively be used. For example, thearrangements of the elements in the diagrams, or the order of executionof the blocks in the diagrams may be changed, or some of the circuitelements in circuit diagrams, and blocks in block/flow diagramsdescribed may be changed, eliminated, or combined. Any elements asillustrated or described may be changed, eliminated, or combined.

In the preceding description, various aspects of the disclosed subjectmatter have been described. For purposes of explanation, specificnumbers, systems and configurations were set forth in order to provide athorough understanding of the subject matter. However, it is apparent toone skilled in the art having the benefit of this disclosure that thesubject matter may be practiced without the specific details. In otherinstances, well-known features, components, or modules were omitted,simplified, combined, or split in order not to obscure the disclosedsubject matter.

Various embodiments of the disclosed subject matter may be implementedin hardware, firmware, software, or combination thereof, and may bedescribed by reference to or in conjunction with program code, such asinstructions, functions, procedures, data structures, logic, applicationprograms, design representations or formats for simulation, emulation,and fabrication of a design, which when accessed by a machine results inthe machine performing tasks, defining abstract data types or low-levelhardware contexts, or producing a result.

Program code may represent hardware using a hardware descriptionlanguage or another functional description language which essentiallyprovides a model of how designed hardware is expected to perform.Program code may be assembly or machine language or hardware-definitionlanguages, or data that may be compiled or interpreted. Furthermore, itis common in the art to speak of software, in one form or another astaking an action or causing a result. Such expressions are merely ashorthand way of stating execution of program code by a processingsystem which causes a processor to perform an action or produce aresult.

Program code may be stored in, for example, one or more volatile ornon-volatile memory devices, such as storage devices or an associatedmachine readable or machine accessible medium including solid-statememory, hard-drives, floppy-disks, optical storage, tapes, flash memory,memory sticks, digital video disks, digital versatile discs (DVDs),etc., as well as more exotic mediums such as machine-accessiblebiological state preserving storage. A machine readable medium mayinclude any tangible mechanism for storing, transmitting, or receivinginformation in a form readable by a machine, such as antennas, opticalfibers, communication interfaces, etc. Program code may be transmittedin the form of packets, serial data, parallel data, etc., and may beused in a compressed or encrypted format.

Program code may be implemented in programs executing on programmablemachines such as mobile or stationary computers, personal digitalassistants, set top boxes, cellular telephones and pagers, and otherelectronic devices, each including a processor, volatile or non-volatilememory readable by the processor, at least one input device or one ormore output devices. Program code may be applied to the data enteredusing the input device to perform the described embodiments and togenerate output information. The output information may be applied toone or more output devices. One of ordinary skill in the art mayappreciate that embodiments of the disclosed subject matter can bepracticed with various computer system configurations, includingmultiprocessor or multiple-core processor systems, minicomputers,mainframe computers, as well as pervasive or miniature computers orprocessors that may be embedded into virtually any device. Embodimentsof the disclosed subject matter can also be practiced in distributedcomputing environments where tasks may be performed by remote processingdevices that are linked through a communications network.

Although operations may be described as a sequential process, some ofthe operations may in fact be performed in parallel, concurrently, or ina distributed environment, and with program code stored locally orremotely for access by single or multi-processor machines. In addition,in some embodiments the order of operations may be rearranged withoutdeparting from the spirit of the disclosed subject matter. Program codemay be used by or in conjunction with embedded controllers.

While the disclosed subject matter has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the subject matter, whichare apparent to persons skilled in the art to which the disclosedsubject matter pertains are deemed to lie within the scope of thedisclosed subject matter. For example, in each illustrated embodimentand each described embodiment, it is to be understood that the diagramsof the figures and the description herein is not intended to indicatethat the illustrated or described devices include all of the componentsshown in a particular figure or described in reference to a particularfigure. In addition, each element may be implemented with logic, whereinthe logic, as referred to herein, can include any suitable hardware(e.g., a processor, among others), software (e.g., an application, amongothers), firmware, or any suitable combination of hardware, software,and firmware, for example.

What is claimed is:
 1. A system comprising: a primary side comprising acharger and a first battery, the first battery to provide power to theprimary side; a secondary side comprising a second battery, the secondbattery to provide power to the secondary side; and hinge resistancebetween the primary side and the secondary side; wherein the charger isto charge the first battery and the second battery; and wherein theprimary side includes a feedback controlled active device in a currentpath of the first battery that compensates for one or more of the hingeresistance, connector resistances, or battery impedances in a currentpath of the second battery.
 2. The system of claim 1, wherein theprimary side comprises a motherboard of the system.
 3. The system ofclaim 1, wherein the first battery is to provide power to a firstdisplay of the system and the second battery is to provide power to asecond display of the system.
 4. The system of claim 1, the feedbackcontrolled active device including a first sense resistor to sensecurrent through a battery current path of the first battery and a secondsense resistor to sense current through a battery current path of thesecond battery.
 5. The system of claim 4, the feedback controlled activedevice including an amplifier and a transistor, the amplifier to adjusta resistance of the transistor so that voltage drops across the firstsense resistor and the second sense resistor are equal during a chargingof the first battery and the second battery.
 6. The system of claim 5,wherein the transistor is a field effect transistor.
 7. The system ofclaim 5, the feedback controlled active device including a secondamplifier to override the first amplifier during a discharging of thefirst battery and the second battery.
 8. The system of claim 7, thesecond amplifier to turn the transistor fully on during the dischargingof the first battery and the second battery.
 9. The system of claim 5,the feedback controlled active device including a bypass resistor acrossthe transistor.
 10. The system of claim 9, wherein the bypass resistoris to be adjusted based on a maximum charge sharing current limit. 11.The system of claim 4, the feedback controlled active device including afirst resistor and a second resistor coupled in series with each other,the series connection of the first resistor and the second resistorcoupled in series to be coupled in parallel with the first senseresistor, wherein resistances of the first resistor and the secondresistor coupled in series with each other can be adjusted to adjustcharging currents of the first battery and the second battery.
 12. Thesystem of claim 1, the feedback controlled active device to balancecharging and discharging of the first battery and the second battery.13. A system comprising: a primary side comprising a charger and a firstbattery, the first battery to provide power to the primary side; asecondary side comprising a second battery, the second battery toprovide power to the secondary side; and hinge resistance between theprimary side and the secondary side; wherein the charger is to chargethe first battery and the second battery; and wherein the secondary sideincludes a feedback controlled boost converter in a current path of thesecond battery that compensates for voltage drops between the firstbattery and the second battery.
 14. The system of claim 13, wherein theprimary side comprises a motherboard of the system.
 15. The system ofclaim 14, wherein the first battery is to provide power to a firstdisplay of the system and the second battery is to provide power to asecond display of the system.
 16. The system of claim 13, the feedbackcontrolled boost converter including a series voltage in the currentpath of the second battery to compensate for voltage drops between thefirst battery and the second battery.
 17. The system of claim 13, thefeedback controlled boost converter including an amplifier todifferentially sense a voltage of the first battery and compare it witha voltage of the second battery.
 18. The system of claim 17, theamplifier to control the boost converter using the amplified differencein voltage.
 19. The system of claim 18, the boost converter to adjust aduty cycle to compensate for a voltage drop between the first batteryand the second battery.
 20. The system of claim 13, wherein if acapacity of the first battery is the same as a capacity of the secondbattery, the feedback controlled boost converter is to discharge thefirst battery and the second battery at equal voltages and at equalcurrents.
 21. The system of claim 13, wherein if a capacity of the firstbattery is not the same as a capacity of the second battery, thefeedback controlled boost converter to adjust a discharge current of thefirst battery and a discharge current of the second battery to beproportional to their respective battery capacities.
 22. The system ofclaim 13, the feedback controlled boost converter including a currentsense amplifier to sense a current of the first battery and to controlthe boost converter in response to the sensed current of the firstbattery.
 23. The system of claim 13, the feedback controlled boostconverter including a current sense amplifier to sense a current of thefirst battery, to sense a current of the second battery, and to controlthe boost converter in response to the sensed current of the firstbattery and the sensed current of the second battery.
 24. The system ofclaim 23, wherein the feedback controlled boost converter is to maintaina discharge current of the first battery and a discharge current of thesecond battery to be equal.
 25. The system of claim 13, wherein thefeedback controlled boost converter is to automatically distributedischarge current to the first battery and to the second batteryirrespective of battery capacities.